Igniter

ABSTRACT

A device specially adapted for igniting model rocket engines which includes a thin wedge-shaped paper or deformable plastic substrate, a thin electrically conductive metal foil on one side of the substrate and a pyrotechnic igniting bead carried on the tip end of the wedge-shaped device. A slit extends from the base of the wedge to a point spaced from the tip end, dividing the foil into two conductor portions which join at the tip end to form a resistance heating portion in thermal contact with the pyrotechnic igniting bead.

1 States 11 1 [111 3,71,12 cAllister [45] W 1973 [5 IGNITER 3,521,5647/1970 Gould et al. 102 497 Inventor: J G. McAllister, x, A 3,546,99712/1970 Gould et a]. 102/497 [73] Assignee: Centuri Engineering Company,Inc., Primary ExaminerRobert F. Stahl Phoenix, Ariz, Attorney-Eric P.Schellin and John A. Robertson [22] Filed: Mar. 23, 1970 [57] ABSTRACT[21] Appl. No.: 21,599

A device specially adapted for igniting model rocket engines whichincludes a thin wedge-shaped paper or [52] US Cl 102/34, 102/497,102/702 A deformable plastic substrate, a thin electrically conduc- 511m. (:1 F42b 15/00, C06d 1/04 tive metal foil on one side of thesubstrate and a py [58] Field of Search 60/256; 102/34, 34.1, technicigniting bead carried on the p end of the 102 342 343 344 34 5 49 7 702wedge-shaped device. A slit extends from the base of the wedge to apoint spaced from the tip end, dividing [56] Refer ce Cit d the foilinto two conductor portions which join at the UNITED STATES PATENTS tipend to form a resistance heating portion in thermal 3,422,763 1/1969Wait 102/497 Contact the pyrotechmc gmtmg bead 3,434,426 3/1969 DeDapper 102/100 4 Claims, 6 Drawing Figures PAIENIEDmas um 3.741. 120

INVENTOR. JACK a. MC ALLISTER ATTORNEYS IGNITER This invention relatesto igniting devices.

More particularly, the invention relates to electric resistance heatingactuated igniting devices.

In a particular aspect, the invention concerns igniting devicesspecially adapted for use in igniting model rocket engines.

Several types of electrically actuated igniters for model rocket enginesare known in the art. The simplest type is a very fine wire formed ofnichrome or other appropriate resistance heating material. A length ofthe wire is merely inserted into the nozzle end of a model rocket engineand the ends of the wire are coupled by means of suitable alligatorclips to a pair of conductors leading to a battery and switch connectedin series. When the switch is closed, the current flowing through theresistance wire causes the wire to heat to a temperature at which itwill ignite the propellant charge of the model rocket engine. Accordingto further improvements, resistance wire igniters are provided with aheat-sensitive pyrotechnic composition in the form of a bead or tubularcoating on a portion of the wire. When the wire is heated, it ignitesthe pyrotechnic composition which, in turn, ignites the propellantcharge of the rocket engine.

According to another prior art technique, a pyrotechnic fuse is insertedinto the nozzle of the model rocket engine and in close proximity to thepropellant charge within the engine. The end of the fuse extendingoutside the engine is ignited by means of a resistance heating wirewrapped around the end of the fuse or maintained in thermal contact withthe fuse by adhesive tape.

The above-described prior art igniters do reduce the safety hazardsinvolved in igniting a rocket engine by making it possible for theoperator to initiate the ignition sequence from a remote position.However, it would be advantageous to provide an igniter device which isless expensive and easier to produce, which is more convenient to useand which provides reliable and prompt ignition of the rocket engine andwhich has a relatively low electrical current requirement.

It is therefore a principal object of the present invention to providean igniting device.

Another object of the invention is to provide an igniting devicespecially adapted for use in igniting solid propellant model rocketengines.

Another object of the invention is to provide a model rocket engineigniting device which can be manufactured economically and which can beused more conveniently than certain of the prior art igniters.

Still another object of the invention is to provide an igniter which hasa low electrical current requirement but which insures prompt andreliable ignition of the rocket engine.

These and other, further and more specific objects and advantages of theinvention will become apparent from the following detailed descriptionthereof and the drawings, in which:

FIG. 1 is a schematic prospective view of a typical model rocket andassociated electrical ignition equipment;

FIG. 2 is a sectional prospective view of a typical model rocket engine;

FIG. 3 is a plan view of a model rocket engine igniter embodying thefeatures of my invention;

FIG. 4 is a sectional view of the igniter of FIG. 3 taken along sectionline 4-4 thereof;

FIG. 5 is a perspective view of the igniter device of FIGS. 3 and 4showing the method of connecting the igniter to the electrical leads ofthe ignition initiating equipment; and

FIG. 6 is a plan view illustrating how the igniter of FIGS. 3-5 may beconveniently manufactured.

Briefly, in accordance with my invention, I provide an electricallyactuated igniter which is specially adapted for use in igniting a solidpropellant model rocket engine although, as will be appreciated by thoseskilled in the art, the igniter could be used for many other purposessuch as igniting various industrial and military pyrotechnic devicessuch as wire-laying rockets and in many other practical applications.

The typical model rocket engine includes an elongate tubular case, arestrictive refractory nozzle disposed in the lower end of the enginecasing and a solid propellant charge disposed within the casing abovethe restrictive nozzle. My igniter device comprises an electricallyinsulating substrate, an electrical resistance heating metal foilcarried on a side of the substrate, the substrate and foil beingdimensioned to permit the tip of the igniter to be inserted into therestrictive nozzle of the rocket engine proximate the solid propellantcharge. The device is preferably shaped and dimensioned to befrictionally engaged by the restrictive nozzle to hold the tip of theigniter in proximity to the propellant charge. However, the utility ofthe device is not restricted to require that it be held in the enginenozzle by frictional engagement and, for example, can be readily securedin the proper operative position by a piece of narrow adhesive tapeinserted between the downwardly extending conductor portions and havingeach end secured to the outside of the engine casing.

The metal foil has a slit therein extending from the base edge of thewedge-shaped substrate to a point spaced from the tip edge thereof,thereby dividing the foil into two conductor portions. The conductorportions join at the tip end of the slit to form a resistance heatingportion. A pyrotechnic igniting bead is carried on the tip end of theigniter and disposed in thermal contact with the resistance heatingportion.

Turning to the drawings, FIG. 1 illustrates a typical model rocket andassociated electrical igniting equipment. The model rocket willgenerally include a tubular body shell 11, appropriate stabilizing fins12 and a noze cone portion 13. The tubular body portion encloses therocket engine contained in the lower end 11a of the body and may containa parachute packed in the upper end 11b of the rocket body which lowersthe nose cone and the rocket back to the earth at the terminal portionof the powered flight period. The electrical leads to the ignitingdevice 14 are connected by means of suitable alligator clips 15 toconductor wires 16 which connect the igniter in series electricalconnection with a battery 17 and an actuating switch 18. When the switch18 is closed, the igniter is actuated, firing the engine. The igniterwires 14 are pulled from the alligator clips 15 as the rocket rises fromthe ground. To better illustrate the principles of my invention, FIG. 2is a sectional perspective view of a typical model rocket engine showingthe tubular engine casing 21, the ceramic restrictive nozzle 22 andsolid propellant charge 23. In the case of a single-stage engine, thecasing will usually contain a delay charge 24, an ejection charge 25 andsuitable wadding 26. The ignition sequence includes the ignition of thepropellant charge which, in turn, ignites the delay charge which, inturn, ignites the ejection charge. When the ejection charge 25 is fired,the nose cone 13 is separated from the body portion 11 of the rocket,pulling the packed parachute out of the end 11b of the rocket body 11.

Referring to FIGS. 3, 4 and 5, my igniter comprises a base or substrateportion 41 formed of a suitable electrically insulating material such ascardboard or plastic. In a preferred embodiment, I employ 0.010 inchthick polyvinylchloride. The substrate material should be deformable sothat the conductor portions of the foil may be separated slightly whenthe alligator clips 15 are attached to the igniter. In a preferredembodiment, the substrate has a slit 31 extending inwardly from the baseedge 32 to facilitate deformation to permit attachment of the clips 15.It is much more convenient to attach the alligator clips 15 to theconductor portions 42a in my igniter device than to the fine nichromewire of leads in several of the prior art igniters.

The substrate 41 carries a thin electrically conductive metal foil 42.The foil 42 has a slit 43 extending from the base edge 32 toward the tipend 33 of the substrate 41. The slit 43 extends to a point within ashort distance of the tip 33, thus dividing the foil 42 into conductorportions 42a which join at the tip 33 to form a resistance heatingportion 42b.

Although the exact dimensions are, of course, not critical, theconvenience of use of my igniter is greatly enhanced if the device isdimensioned to be held within the engine casing by frictional engagementbetween the side edges 44 of the igniter and the nozzle 22, such thatthe tip end 33 of the igniter is in close proximity to, or eventouching, the solid propellant charge 23. Any suitable resistanceheating metal foil may be employed such as nichrome foil, or aspresently preferred, steel foil of a thickness of 0.001 inch. The foilmay be adhesively attached to the substrate or by any other suitablemeans.

The igniter devices of FIGS. 3-5 may be conveniently manufactured bystamping and die-cutting a sheet of the foil-covered substrate as shownin FIG. 6 and thereafter dipping the tips 33 into a suitable plasticizedpyrotechnic flare composition to form the igniting beads 61. Thedimensions shown on FIG. 6 are, of course, nonlimiting and merelyillustrate a convenient size of the igniter which is adapted to befrictionally engaged within the nozzles of certain present standardmodel rocket engines which are generally available in the industry.

Suitable pyrotechnic igniting compositions are well known in the artand, for example, in a presently preferred embodiment, I employ amixture as follows:

Parts by Wt. 2 Manganese Dioxide lOO Potassium Chlorate 25 Iron PowderContact Cement The foregoing ingredients are thoroughly mixed withsufficient contact cement thinner to achieve the desired degree ofplasticity to permit coating the tips of the igniters by dipping theminto the mixture to form the pyrotechnic igniter head on the tip.

I claim:

1. An electrically actuated igniter specially adapted for use inigniting a solid propellant rocket engine, said engine including anelongate tubular casing,

a restrictive refractory nozzle disposed in the lower end of said enginecasing, and

a solid propellant charge disposed within said casing above saidrestrictive nozzle,

which igniter comprises:

a. an electrically insulating substrate;

b. an electrical resistance heating metal foil carried on a side of saidsubstrate;

c. said substrate and foil carried thereon being wedge-shaped to permitthe narrower tip thereof to be inserted into said restrictive nozzleproximate said solid propellant charge;

d. said metal foil having a slit therein extending from the base edge ofsaid wedge-shaped substrate to a point spaced from the tip edge thereof,said slit dividing said foil into two conductor portions, each conductorportion joining at the tip end of said slit, forming a resistanceheating portion of foil, and

e. a pyrotechnic igniting bead carried on the tip end of said igniterand disposed in thermal contact with said resistance heating portion.

2. lgniter of claim 1 wherein said substrate is deformable and has aslit extending inwardly from the base edge thereof a distance sufficientto separate the ends of said conductor portions.

3. Igniter of claim 1 which is dimensioned to be frictionally engaged bysaid nozzle to hold said tip in said proximate position.

4. A method of manufacturing igniter squibs comprising:

a. forming a laminate structure of an electrically insulating substratesheet, and an electrical resistance heating metal foil carried on a sideof said substrate sheet;

b. slitting said foil from one edge of said laminate sheet to a pointspaced from another edge thereof, said slit thereby dividing said foilinto two conductor portions, each conductor portion joining at the endof said slit spaced from said side, forming a resistance heating portionof said foil; and

c. coating said resistance heating portion with a heatsensitivepyrotechnic igniting composition.

4 i a a

1. An electrically actuated igniter specially adapted for use inigniting a solid propellant rocket engine, said engine including anelongate tubular casing, a restrictive refractory nozzle disposed in thelower end of said engine casing, and a solid propellant charge disposedwithin said casing above said restrictive nozzle, which ignitercomprises: a. an electrically insulating substrate; b. an electricalresistance heating metal foil carried on a side of said substrate; c.said substrate and foil carried thereon being wedge-shaped to permit thenarrower tip thereof to be inserted into said restrictive nozzleproximate said solid propellant charge; d. said metal foil having a slittherein extending from the base edge of said wedge-shaped substrate to apoint spaced from the tip edge thereof, said slit dividing said foilinto two conductor portions, each conductor portion joining at the tipend of said slit, forming a resistance heating portion of foil, and e. apyrotechnic igniting bead carried on the tip end of said igniter anddisposed in thermal contact with said resistance heating portion. 2.Igniter of claim 1 wherein said substrate is deformable and has a slitextending inwardly from the base edge thereof a distance sufficient toseparate the ends of said conductor portions.
 3. Igniter of claim 1which is dimensioned to be frictionally engaged by said nozzle to holdsaid tip in said proximate position.
 4. A method of manufacturingigniter squibs comprising: a. forming a laminate structure of anelectrically insulating substrate sheet, and an electrical resistanceheating metal foil carried on a side of said substrate sheet; b.slitting said foil from one edge of said laminate sheet to a pointspaced from another edge thereof, said slit thereby dividing said foilinto two conductor portions, each conductor portion joining at the endof said slit spaced from said side, forming a resistance heating portionof said foil; and c. coating said resistance heating portion with aheat-sensitive pyrotechnic igniting composition.